Do You Need to Put Anything Between Plywood & a Backer Board for a Countertop?

General Information

• Backer board provides a level surface that new countertops can adhere to. Some countertop under-surfaces use plywood and backer board, while others require only the use of plywood. In general, some type of adhesive or other object separates plywood and cement backer board. Some backer boards require the use of dry-set mortar, modified thinset or mastic. Nails or screws then firmly secure the backer board in place. Other backer boards require the use of felt, which is stapled into place. The material that separates the plywood from the countertop depends on the recommendation of the backer board manufacturer and the maker of the countertop you install.

Tile Countertops

• Using a backer board with tile countertop saves you a tremendous amount of work by replacing the need for a wire mesh system. You may need to place a water-resistant membrane between the plywood and backer board to prevent moisture damage. Any exposed plywood, such as the area near the edges of walls or the sink, also need a coating of liquid waterproofing. Spread thinset mortar on the plywood to adhere the backer board to it.

Concrete Countertops

• Concrete countertops may not need anything besides plywood to support them. However, if one side of a concrete countertop rests slightly higher than the other side, you may need to drill metal screws up into the plywood. A liquid adhesive will help a countertop adhere to plywood, without the need for backer board. If your base cabinets can't support the weight of concrete countertops, you may need to add additional plywood to the existing sheet to achieve a depth of three-quarters of an inch. You can also add vertical supports on top of the plywood.

Granite Countertops

• Use a moisture barrier in conjunction with a granite slab countertop. A two-part epoxy helps granite adhere to a subcounter. Spread one-eighth-inch thinset mortar over plywood for use with granite tiles. Place the backer board over the mortar and nail it in place with 1-inch shingle nails. The backer board helps provide a level surface for your tiling job.

Butcher Block Countertops

• Butcher block countertops are not labor intensive, relatively speaking. Add a kitchen and bath sealant to make the countertop adhere. Drill deck screws from inside the cabinetry through the plywood support and the butcher block to safely secure it in place.